Backlight system and liquid crystal display using the same

ABSTRACT

A backlight system ( 100 ) in accordance with the present invention includes a plurality of light sources ( 110 ) for emitting light beams and a light guide plate ( 120 ) for receiving the light beams emitted by the light sources. The light guide plate includes a light input surface ( 121 ) and a light output surface ( 122 ) joining the light input surface. The light input surface has a plurality of recesses ( 124 ) therein. The recesses have cylindrical surfaces, each having a specific curvature, and the light beams emitted by the light sources pass through the cylindrical surfaces orthogonally. Since nearly all of the light beams enter into the light guide plate with few being reflected at the light input surface, the backlight system is highly efficient in light utilization.

BACKROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a backlight device andparticularly to an edge light type backlight device for use in a liquidcrystal display (LCD) or the like.

[0003] 2. Description of Related Art

[0004] An LCD device comprises, for example, a liquid crystal displaypanel and a backlight system mounted under the liquid crystal displaypanel for supplying light beams thereto. The backlight system mainlycomprises a light source and a light guide plate, wherein the lightguide plate is made of a transparent acrylic plastic plate and is usedfor guiding the light beams emitted by the light source to uniformlyilluminate the liquid crystal display panel.

[0005] The light source emits light beams into the light guide plate,wherein the light beams are totally internally reflected. In order todiffuse the light beams and emit them uniformly from a top surface ofthe light guide plate, protrusions or recesses are located on a bottomsurface of the light guide plate, or a pattern of light diffusion dotsare formed on the bottom surface of the light guide plate.

[0006] Referring to FIG. 7, a conventional backlight system 9 comprisesa light source 40, which can be light emitting diodes, miniature bulbs,or other point light sources, a cage 30 having a reflective coating (notshown) thereon, a light guide plate 10, and a translucent sheet 20. Thecage 30 has a locating notch 31 therein. The light guide plate 10comprises a light input surface 11 and a light output surface 12.

[0007] In assembly, the light source 40 is arranged in the locatingnotch 31 of the cage 30, and the light guide plate 10 is accommodated inthe cage 30. The light input surface 11 of the light guide plate 10 isadjacent to the light sources 40. The translucent sheet 20 is placedupon the light guide plate 10.

[0008] In operation, light beams emitted by the light source 40 passthrough the light input surface 11 and enter into the light guide plate10, and then are transmitted out from the light output surface 12 of thelight guide plate 10. After that, the light beams pass through thetranslucent sheet 20 to illuminate an LCD panel.

[0009] However, the light source 40 has a certain emitting angle. Forexample, a light emitting diode used as the light source 40 emits lightbeams with an emitting angle in a range of 30° to 130°. Since the lightinput surface 11 is planar, when the light beams emitted by the lightsource 40 impinge on the input surface 11, they are partly reflected,and partly transmitted. Not all the light beams enter into the lightguide plate, thus the efficient utilization of the light beams isdecreased, and the brightness of the light guide plate 10 is alsodecreased.

[0010] It is desirable to provide an improved backlight system for aliquid crystal display, which overcomes the above problems.

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide a backlightsystem with high efficient utilization of the generated light beams.

[0012] Another object of the present invention is to provide a backlightsystem with high brightness.

[0013] A backlight system in accordance with the present inventioncomprises a plurality of light sources for emitting light beams and alight guide plate for receiving the light beams emitted by the lightsources. The light guide plate comprises a light input surface and alight output surface joining the light input surface. The light inputsurface comprises a plurality of recesses therein, which have acylindrical surface with a certain curvature. Each cylindrical surfaceis opposite to a corresponding light source, and the light beams emittedby the light source pass through the cylindrical surface orthogonally.

[0014] Other objects, advantages, and novel features of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view of a backlight system according tothe present invention;

[0016]FIG. 2 is a bottom view of the backlight system in FIG. 1;

[0017]FIG. 3 is a perspective view of a second embodiment of a backlightsystem according to the present invention;

[0018]FIG. 4 is a bottom view of the backlight system in FIG. 3;

[0019]FIG. 5 is a perspective view of a third embodiment of a backlightsystem according to the present invention;

[0020]FIG. 6 is a schematic view of a liquid crystal display deviceusing the backlight system of FIG. 5; and

[0021]FIG. 7 is a conventional backlight system.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0022] Referring to FIG. 1, a backlight system 100 in accordance withthe present invention is used to illuminate a liquid crystal displaydevice. The backlight system 100 comprises a plurality of light sources110 and a light guide plate 120. The light sources 110 emit light, andthe light guide plate 120 is arranged adjacent to the light sources 110to receive the light emitted therefrom.

[0023] The light sources 110 can be light emitting diodes, miniaturebulbs, or the like. The luminance of the light sources 110 can beadjusted.

[0024] Referring also to FIG. 2, the light guide plate 120 is shaped asa planar plate and can be made of a transparent acrylic plastic. Thelight guide plate 120 comprises a light input surface 121, a lightoutput surface 122 joining the light input surface 121, and a bottomsurface 123 opposite to the light output surface 122. The light inputsurface 121 comprises a plurality of recesses 124 therein. Each recess124 has a cylindrical surface with a specific curvature, each recessbeing respectively opposite to a corresponding light source 110. Eachlight source 110 is arranged at the center of a correspondingcylindrical surface where that center is defined as the point which isequidistant from all points of that cylindrical surface, thus, the lightbeams emitted by each light source 110 pass through the cylindricalsurface orthogonally. Therefore, few light beams are reflected.Moreover, the angle subtended by the cylindrical surface at each lightsource 110 is equal to the emitting angle of the light sources 110.Therefore, almost all the light beams emitted by each light source 110pass through the cylindrical surface of its corresponding recess 124orthogonally and are transmitted into the light guide plate 120. Thebottom surface 123 of the light guide plate 120 has a dot-pattern 127thereon, for improving the uniformity of light emitted from the lightguide plate 120. The dot-pattern 127 can be manufactured by printingreflective dots (not labeled) or by molding projections (not labeled) onthe bottom surface 123. The size of the dots in the dot-pattern 127increase in a direction away from the light input surface 121. The shapeof each molded projection can be hemispherical, cylindrical, square orcone-shape. Moreover, a plurality of v-cut grooves (not show) can beformed in the bottom surface 123 to substitute for the dot-pattern 127.

[0025] Turning to FIGS. 3-4, a second embodiment of a backlight system200 in accordance with the present invention is similar to the backlightsystem 100. The difference therebetween is that the backlight system 200comprises a light guide plate 220, which includes two light inputsurfaces 221. Each light input surface 221 has a plurality of recesses224 therein. Each light input surface 221 further comprises ananti-reflective film 225 thereon, which covers the light input surface221 and the recesses 224. The anti-reflective films 225 can improve anefficient utilization of the light beams emitted by the light sources210 by transmitting more of the light beams into the light guide plate220. The bottom surface 223 has a dot-pattern 227 thereon, which hasregularly arranged dots (not labeled) to enhance the opticalcharacteristics of the light guide plate 200.

[0026]FIG. 5 shows a third embodiment of a backlight system 300 inaccordance with the present invention. The backlight system 300comprises a plurality of light sources 310 and a light guide plate 320,wherein the light guide plate 320 is in a shape of a wedge. The lightguide plate 320 comprises a light input surface 321, a light outputsurface 322 and a bottom surface 323 opposite to the light outputsurface 322. The light input surface 321 comprises a plurality ofrecesses 324 therein. The bottom surface 323 has a reflective coating(not show) thereon, which reflects the light beams to prevent the lightbeams from transmitting out of the light guide plate 320 through thebottom surface 323.

[0027]FIG. 6 shows an LCD device 90 using the backlight system 300. Itcould instead, of course, use either of the backlight systems 200, 100.The LCD device 90 comprises the backlight system 300, a diffusion sheet93, a prism sheet 92 and a liquid crystal panel 91, which are arrangedin order. The backlight system 300 is arranged under the liquid crystalpanel 91, and comprises a plurality of light sources 310 and a lightguide plate 320. In operation, light beams emitted by the light sources310 enter into the light guide plate 320, are then transmitted out fromthe light output surface 322, and are then passed through the diffusionsheet 93 and the prism sheet 92 to illuminate the liquid crystal panel91.

[0028] Advantages of the present invention over the prior art includethe following. First, the light beams emitted pass through thecylindrical surfaces orthogonally. As a result, nearly all of the lightbeams enter into the light guide plate, so the backlight system ishighly efficient in light utilization. Second, few light beams arereflected, therefore, the backlight system has a high brightness.

[0029] It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size, and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

What is claimed is:
 1. A backlight system for a display devicecomprising: a plurality of light sources for emitting light beams; and alight guide plate for receiving the light beams emitted by the lightsources, which light guide plate comprises a light input surface and alight output surface joining the light input surface; wherein the lightinput surface has a plurality of recesses defined therein, the recesseseach having a cylindrical surface with a specific curvature, each of thecylindrical surfaces being opposite to a corresponding light source, sothat the light beams emitted by the light source pass through thecylindrical surface orthogonally.
 2. The backlight system as claimed inclaim 1, wherein each light source is arranged at a center of itscorresponding cylindrical surface.
 3. The backlight system as claimed inclaim 1, wherein the angle subtended by each surface at the location ofits corresponding light source is fixed.
 4. The backlight system asclaimed in claim 3, wherein each light source has a specific emittingangle.
 5. The backlight system as claimed in claim 4, wherein the anglesubtended by each cylindrical at the location of its corresponding lightsource is equal to the emitting angle of the light source.
 6. Thebacklight system as claimed in claim 1, wherein the light sources can belight emitting diodes or miniature bulbs.
 7. The backlight system asclaimed in claim 1, wherein the light guide plate can be a planar plateor a wedge plate.
 8. The backlight system as claimed in claim 1, whereinthe light input surface has an anti-reflection coating thereon.
 9. Thebacklight system as claimed in claim 1, wherein the light guide platefurther comprises a bottom surface opposite to the light output surface.10. The backlight system as claimed in claim 9, wherein the bottomsurface has a dot-pattern thereon.
 11. The backlight system as claimedin claim 9, wherein the bottom surface has a plurality of v-cut groovestherein.
 12. The backlight system as claimed in claim 1, furthercomprising another light input surface, which has a plurality ofrecesses therein.
 13. A liquid crystal display comprising: a liquidcrystal panel; and a backlight system arranged under the liquid crystalpanel for illuminating it, the backlight system comprising: a pluralityof light sources for emitting light beams; and a light guide plate forreceiving the light beams emitted by the light sources, which lightguide plate comprises a light input surface and a light output surfacejoining the light input surface; wherein the light input surface has aplurality of recesses defined therein, the recesses each havecylindrical surfaces defining a certain curvature, and each cylindricalsurface is opposite to a corresponding light source, and the light beamsemitted by the light source pass through the corresponding cylindricalsurface orthogonally.
 14. The liquid crystal display as claimed in claim13, wherein the light sources are each arranged at a center of theircorresponding cylindrical surfaces.
 15. The liquid crystal display asclaimed in claim 13, wherein the cylindrical surfaces each subtend acertain angle at the corresponding light source.
 16. The liquid crystaldisplay as claimed in claim 15, wherein the light sources emit within afixed emitting angle.
 17. The liquid crystal display as claimed in claim16, wherein the angle subtended by each of the cylindrical surfaces atthe corresponding light source is equal to the emitting angle of thelight source.
 18. The liquid crystal display as claimed in claim 13,wherein the light sources can be light emitting diodes or miniaturebulbs.
 19. The liquid crystal display as claimed in claim 13, whereinthe light guide plate can be a planar plate or a wedge plate.
 20. Theliquid crystal display as claimed in claim 13, wherein the light inputsurface has an anti-reflection coating thereon.
 21. The liquid crystaldisplay as claimed in claim 13, wherein the light guide plate furthercomprises a bottom surface opposite to the light output surface.
 22. Theliquid crystal display as claimed in claim 21, wherein the bottomsurface has a dot-pattern thereon.
 23. The liquid crystal display asclaimed in claim 21, wherein the bottom surface has a plurality of v-cutgrooves therein.
 24. The liquid crystal display as claimed in claim 13,further comprising another light input surface, which has a plurality ofrecesses therein.
 25. A liquid crystal display comprising: a pluralityof light sources for emitting light beams; and a light guide platedefining a main light output face and a light input face essentiallyperpendicular to said light output face, said light sources positionedbeside said light guide plate and facing said light input face; whereinsaid light input face defines a plurality of concaves respectivelyaligned with the corresponding light sources along a directionperpendicular to said light input face, thereby the light beam derivedfrom each of said light sources distributes substantially even intensityon the corresponding concave due to similar distances between variousportions of said concave and the same corresponding light source.